ORLANDO, Fla. — It may seem obvious, but now there’s proof: Exercise of moderate intensity can help older people stay mobile and independent, according to the largest clinical trial ever done on the issue.

The study, presented Tuesday at the annual meeting of the American College of Sports Medicine in Orlando, Fla., involved eight field centers.

A physical activity program consisting of aerobic, resistance, and flexibility exercises significantly reduced the risk of a major disability, researchers found.

“Until this study, we didn’t have the proof necessary to say that daily exercise, sustained over several years, truly can prevent loss of mobility,” said Anne Newman, chairman of the epidemiology department at the University of Pittsburgh’s graduate school of public health, which participated in the study. “Doctors can now feel confident that moderate physical activity improves the independence and mobility of older adults.”

For purposes of the Lifestyle Interventions and Independence for Elders study, a “major mobility disability” was defined as an inability to walk 400 meters, or about a quarter of a mile.

Researchers, led by Marco Pahor of the University of Florida Institute on Aging in Gainesville, randomly assigned 1,635 seniors ages 70 to 89 who were able to walk a quarter of a mile either to the exercise program or to a health education program consisting of workshops and upper-extremity stretching.

Moderate physical activity helped aging adults maintain their ability to walk at a rate 18 percent higher than older adults who did not exercise, the study showed.

Moreover, there was a 28 percent reduction in people permanently losing the ability to walk easily.

“This large impact on reducing persistent disability is important,” Dr. Newman said. “Beyond simply maintaining mobility, this shows that we can repair a deficit through physical activity.”

When recruited to the study, participants could walk a quarter mile in 15 minutes, but were at risk for losing that ability.

The benefit of physical activity was greater for the seniors who began the study with the lowest physical function, researchers found.

Patients with low physical activity are not often recruited for large studies, Dr. Pahor said. The LIFE study is important because it provides data on an understudied group.

The exercise program consisted of walking for 150 minutes a week as well as doing strength exercises consisting of leg lifts with ankle weights from a seated position. They did this for two years.

One participant who saw results was Josephine Scott, 77, of Pittsburgh.

“I’m so grateful and thankful that I got into this study,” she said.

She said she hadn’t exercised regularly before taking part in the LIFE study. Since it ended, she’s been walking regularly with other women in the evenings around her apartment complex. In fact, her exercise program has helped her stave off knee replacement, Ms. Scott said.

During the 2½ years of the trial, more than 30 percent of participants in the exercise program and 35.5 percent in the health education group experienced major mobility disability.

Death followed persistent inability to walk 400 meters for 14.7 percent in the physical activity group; 19.8 percent in the education group.

However, more “serious adverse events” — any health event that required emergency care — were experienced by seniors in the physical activity group (49.4 percent) than in the education group (45.7 percent).

“There was not a significant difference between the two groups,” Dr. Newman said. “There was no increase in events that could be caused by exercise such as chest pain or falls.”

But it was somewhat of a surprise.

“We had expected to see fewer events in the more active group,” she said. “The fact that we did not could be an unmasking of symptoms,” or simply because the more active group had more opportunities to report adverse events.

The LIFE study is published in the current edition of the Journal of the American Medical Association.

Block News Alliance consists of The Blade and the Pittsburgh Post-Gazette. Jack Kelly is a reporter for the Post-Gazette.